Five consecutive MV patients with COPD were compared with five consecutive MV patients with no known pulmonary disease. Using custom-designed software the vibration signals were fitted to a mathematical function and a gray level frame was constructed. At peak inspiration and expiration, spatial areas of the images were captured and the total area of the image calculated using ImageJ Software.

In patients with normal lungs, the spatial distribution of the maximal signal expiratory vibration response image was lower than the maximal signal during inspiration. The mean decrease in area was 8103 pixels + 20,606 (P = 0.01) (Table 1). In patients with COPD the spatial distribution of the maximal signal expiratory vibration response image during expiration was higher than the maximal signal inspiratory image. The mean increase in area was 19,214 pixels + 6552 (P = 0.03) (Table 2).

The increase in the image area during the expiratory phase in COPD patients may reflect increased airflow resistance causing increased vibration energy. Air trapping and auto-PEEP are other possible mechanisms accounting for the expiratory increase in image area.